1. Field of the Invention
The present invention relates to a new and improved drive for a textile machine. The invention of the present development is particularly advantageous for use in conjunction with drafting arrangements or units in so-called preparatory departments of spinning mills, for example, in draw frames or combing machines.
2. Discussion of the Background and Material Information
It is known for quite some time in the textile art to compensate, especially at so-called autoleveller draw frames, fluctuations in the mass of a sliver which is subsequently to be spun by the controlled alteration of the draft in a draw frame.
In this connection it is also known that the most difficult problems of the process arise during the run-up-to-speed or start-up and the braking of the draw frame. The significance of such run-up-to-speed and braking or stopping of the draw frame increases with ever increasing delivery velocities or speeds, with increasing productivity, of the relevant machine. With a normal delivery velocity or speed of 800 m/min. the run-up-to-speed and braking intervals, respectively, for a draw frame amounts to approximately 1 to 3 seconds. If there is produced a faulty sliver within this time interval because of problems which have arisen in a regulation circuit of the draw frame, then these faults or defects in the sliver, during the subsequent spinning of a fine yarn, can detrimentally affect a yarn length of about 700 to 2000 meters.
The sliver which is processed in the draw frame must be deposited into a so-called can so that such sliver can be transported between different processing stages. After the filling of a can with sliver the draw frame must be briefly stopped in order to exchange the filled can for an empty can, thus requiring a braking interval followed by a run-up-to-speed interval at the draw frame.
German Patent Publication No. 2,650,287, published May 3, 1978, identified the problems of the run-up-to-speed and braking times of a draw frame. However, the solutions proposed therein are exclusively concerned with the transition between the run-up-to speed and the normal operation of the draw frame and the transition between the normal operation and the braking or bringing to standstill of the draw frame. Furthermore, it has been assumed that the sliver draft can be maintained constant during the run-up-to-speed and braking of the draw frame.
In the commonly assigned European Patent No. 0,038,927, published Nov. 4, 1981, there was recognized the necessity of continuing to regulate the sliver draft also during the run-up-to-speed and braking phases of the draw frame. Indeed, it was necessary to increase the "inertia" of the regulation circuit during the run-up-to-speed and braking of the draw frame, in order to overcome regulation problems. This solution mitigates the effects of the total problem without, however, eliminating the same.
European Patent No. 0,141,505, published May 15, 1985, also addresses these problems. The proposed solution suggests that at the "worst" operating times, namely, just prior to and after standstill of the machine, the drive system should be "suddenly" started and stopped, respectively.
It is also known from the commonly assigned European Patent No. 0,355,557, published Feb. 28, 1990, to individually drive the cylinders of a drafting arrangement by position-regulated motors. Amplification of this concept for the drive of a draw frame also has been disclosed in the commonly assigned, copending U.S. application Ser. No. 07/885,245, filed May 20, 1992 and entitled "DRAFTING ARRANGEMENT WITH FEEDBACK DRIVE GROUPS", to which reference may be readily had and the disclosure of which is incorporated herein in its entirety by reference.